The focus of this research project is the elucidation of the pathways by which iron is assimilated, transported, stored, and utilized by the developing erythrocyte. The cell model being used is the rabbit reticulocyte. In the past we have emphasized a study of methodologies used in reticulocyte studies and the mobilization of iron from specifically labeled 59Fe-ghosts by unlabeled lysate. We are completing a project in which the possible involvement of metallothionein in iron transport is examined. The results are negative. The apometallothionein that we prepared is neither able to bind iron presented chemically or that bound to specifically labeled 59Fe-ghosts. Our studies on the exchange of iron by ferritin in reticulocyte lysate have been broadened in scope. We have continued to find little or no evidence for the donation of iron by ferritin for heme synthesis in either reticulocyte or bone marrow cell lysate. We are now examining the uptake of iron by ferritin in lysate. This system may not be as complex as that of iron incorporation into heme and thus may allow a better opportunity to approach the question of cytoplasmic transport agents. We shall attempt to answer some possible procedural problems in the area including development of a test to distinguish between iron bound specifically and non-specifically to ferritin, and the development of a test to rapidly analyze ferritin associated radioactivity in a complex mixture. We shall also examine the mechanism of iron deposition in ferritin in the presence and absence of lysate, and attempt to establish the means by which iron is transported from the plasmalema to the ferritin.